This is a fault in the order profile, and can be due to any of:
Problems with encryption
Inadvertently setting the same variable twice on the form, causing problems due to the embedded null.
Changing the checkout profile and not testing properly under all conditions.
On earlier versions of MiniVend, the demo order profile was placed in an outboard file. On newer versions, it is embedded right in the checkout page. Try replacing [set checkout_profile] with:
[set checkout_profile]
&final=yes
&set=mv_Junk 1
[/set]
If the order completes, then you have a problem in your profile. Also,
check the RequiredFields directive in catalog.cfg, as that is set to name in the demo. If the name variable is blank, then you will find that the order doesn't complete.
The order profile must not have non-blank lines that don't contain valid check procedures (excluding comments). If you are using a Perl routine in the profile, as above, you must take care that the routine returns a valid check routine.